The answer is always steam turbines, because nothing else approaches the practical efficiency of steam turbines when it comes to converting heat to electrical power.
But that is the thing. Pure steam turbine based power have been dead since the 80's with the advent of the combined cycle gas turbine power plants. You get pure mechanical power from the gas turbine and then a tiny steam side to harness the last efficiency gains.
That cost difference is the reason coal has died out, it's simply not economical to run a large steam turbine.
I agree with you in general that it is unlikely that fusion will be cost competitive, but the last time I checked we still got a very large fraction of our power from coal, despite the steam.
Yes, there are financial structural reasons coal is still used. They amount to institutionalized sunk-cost fallacy. Those will take decades to root out.
Sorry to break it to you, but coal is still the largest electricity source with 36.7%. Over the last 20 years its output went from 5.8PW to 10PW (yes, that's petawatts). So, nowhere near "has died out".
I should definitely have prefaced it with the caveat regarding availability of natural gas infrastructure. Gas is cheaper, when you have the infrastructure in place. Less developed countries does not have that luxury, and therefore choose coal because it was pretty much the only thing available until the current renewable boom.
Today we also have LNG, but that seems to mostly be about energy independence. Russia can't simply turn off the tap for Lithuania or Poland, because they have a more pricy alternative method of delivery.
For reference see the dramatic decrease of coal in the US in favor of natural gas.
